In the past, brake bands of the type presently contemplated have been in widespread use. One conventional brake band design incorporates forged brackets which are butt-welded to the free ends of the band. The brackets have required machining operations. Such bands have been satisfactory in use. However, they are relatively high in cost and there has been a desire to produce a brake band which is effective in use but of lower cost.
One proposed construction is illustrated in U.S. Pat. No. 3399749. In this construction, stamped brackets are welded on the outer surfaces adjacent the free ends of the band. A lug is folded upwardly from the material of the bracket. This lug forms abutment structure for the actuating struts.
Several problems have been encountered with such structures. The upstanding nature of the lugs inherently results in a bending force being applied to the lugs. This has resulted in failure of lugs during use of the band. Additionally, the resulting lifting force has caused, in some cases, separation of the bracket from the band at the weld points. Further, there has been excessive toe-in at the ends of the bracket resulting in premature wearing of the friction material provided on the working surface of the band.
In accordance with the present invention a brake band structure is provided incorporating the desirable cost-saving feature of welding brackets to the surface of the free ends of the brake band while at the same time providing a brake band which is as durable and effective in use as previous forged constructions.
A recess is provided on each bracket. The actuating struts are received in the recesses and abut directly against end portions of the recesses. The force that is applied is substantially a line contact force in a direction substantially tangential to the circle defined by the drum. This inherently reduces bending forces.
Additionally, by this construction, the material in front of the actuating element is substantially under pure compression while material behind is in substantially pure tension. The weld points are in substantially pure shear. No area of the bracket is under any substantial turning force. This minimizes possible failure of the bracket and also minimizes any forces tending to lift the bracket from the band.
Additionally, toe-in of the free ends of the band is minimized. The actuating struts are applied at substantially the outer surface of the band material. This places the actuating struts closer to the drum surface thereby reducing turning movement of the brake band with resultant minimizing of toe-in at the free ends of the band. Further, in absence of a lug, there is no additional force caused by the bending moment applied to the lug which, in the past, has aggravated the problem of toe-in. Repeated toe-in also results in fatigue of the band material which, in some cases, causes the band itself to fail.